Genome characterization of Botrytis virus F, a flexuous rod-shaped mycovirus resembling plant ‘potex-like’ viruses

Abstract

This study reports the first sequence of a flexuous rod-shaped mycovirus and also the first molecular characterization of a virus that infects the plant-pathogenic fungus Botrytis cinerea. The mycovirus Botrytis virus F (BVF) contains an ssRNA genome of 6827 nucleotides and a poly(A) tract at or very near the 3′ terminus. Computer analysis of the genomic cDNA sequence of BVF revealed two potential open reading frames (ORFs) encoding proteins of 212 kDa (ORF1) and 32 kDa (ORF2). ORF1 showed significant sequence identity to the RNA-dependent RNA polymerase (RdRp)-containing proteins of plant ‘tymo-’ and ‘potex-like’ viruses. However, the ORF1 protein contained an opal putative readthrough codon between the helicase and RdRp regions, a feature not seen in this position in ‘tymo-’ and ‘potex-like’ replicases sequenced to date. ORF2 shared amino acid similarity with coat proteins of plant ‘potex-like’ viruses. Three untranslated regions were present in the genome, comprising a region of 63 nucleotides preceding the initiation codon of ORF1, a 93 nucleotide stretch between ORFs 1 and 2 and a 3′-terminal region of 70 nucleotides preceding the poly(A) tract. The nucleotide sequence of a putative defective RNA (D-RNA) of 829 nucleotides was also determined. The D-RNA contained one potential ORF comprising the N-terminal region of the replicase fused in-frame to the C-terminal region of the coat protein. It is proposed that the mycovirus BVF belongs to a new, as yet unassigned genus in the plant ‘potex-like’ virus group.